Back in 1950, during a lunch break at the Los Alamos National Laboratory, several scientists were trading wisecracks about a recent spate of UFO reports when Nobel Prize-winning physicist Enrico Fermi offered an observation that has echoed through the decades. Given the number of places where life could exist in the vast universe, and the length of time it has had to evolve, the skies ought to be teeming with beings from advanced, space-faring civilizations — but nothing incontrovertible has shown up. You have to wonder, as Fermi did, “Where is everybody?”

His colleagues chuckled, but the “Fermi paradox” perfectly frames the profound absurdity of the search for life beyond Earth. Humans have beamed beacons into space, robotically visited every world in the solar system and discovered thousands of planets circling stars far from our own. Yet all we’ve encountered is a chilly void.

“The Close Encounters Man: How One Man Made the World Believe in UFOs,” by Mark O'Connell (Dey Street)

Three new books approach the mystery from distinctly different perspectives: the unlikely believer in UFOs, the visionary dedicated to rigorous investigation and the cadre of scientists who still plug away at the problem, probing the universe for an answer.

In “The Close Encounters Man: How One Man Made the World Believe in UFOs,” screenwriter Mark O’Connell recounts the gradual evolution of J. Allen Hynek, an Air Force astronomer, from UFO debunker to believer. Hynek’s tale unfolds a few years before Fermi posed his question, when aliens were much on the minds of Americans. In the summer of 1947, a Boise businessman piloting a small plane across the Cascade Mountains spotted a chain of unidentified flying objects weaving among the peaks. Shortly after, Alabamians reported that brilliant lights appeared over an airfield in Montgomery. Then a swarm of wingless machines was spotted in Maine.

Baffled by these bizarre accounts, the Air Force decided that someone had to sort through all the sightings — if only to prove that they weren’t really extraterrestrials.

So they hired Hynek, an alum of the University of Chicago and a former civilian scientist for the Navy who previously was best known for studying the evolution of stars. Methodical and undogmatic, Hynek could not have been further from the kooky, paranoid stereotype of a UFO enthusiast. He seemed to be exactly the man who could be counted on to dismiss the phenomenon.

Instead, he became its biggest advocate.

“I was somewhat like the proverbial ‘innocent bystander who got shot,’ ” Hynek would later say.

After researching thousands of UFO reports, many from apparently credible witnesses, Hynek became convinced that a significant fraction of sightings could not be explained by current science.

The Air Force, however, disagreed. In 1970 it discontinued its UFO investigations, having concluded that the phenomenon was largely a result of pranksters, psychological experiences and tricks of light.

Undeterred, Hynek established his own Center for UFO Studies and developed a system for classifying these “close encounters” that inspired the 1977 film “Close Encounters of the Third Kind.” Hynek died in 1986 still convinced that UFOs were something “exotic.”

It’s clear that O’Connell, who maintains a UFO blog of his own, wants readers to come away from his book agreeing with Hynek. He derides mainstream astronomers who mock UFOlogy as pseudoscience and reserves special venom for Carl Sagan, who spoke so eloquently about the potential for life in the universe but was unwilling to believe that extraterrestrials might have visited Earth.

I’m inclined to side with Sagan — the human mind is far too easily deceived for this science reporter to believe that rogue aliens offer the most persuasive explanation for strange apparitions in the skies. If there really are advanced beings out there, traversing the universe at the speed of light, it seems unlikely that scaring suburbanites and confusing livestock are the best uses of their time.

But reading “The Close Encounters Man” does engender respect for its subject. “Hynek was a rational person looking at an irrational subject,” James Oberg, a science journalist, NASA engineer and longtime UFO doubter, tells O’Connell. He approached the UFO problem as a scientist would. And although aliens didn’t actually invade America, Hynek — with a little help from Steven Spielberg — helped them invade the American psyche. He got us thinking about encounters with ET, paving the way for a more scientific approach to the search for extraterrestrial intelligence, or SETI.

Shortly after the Air Force gave up on UFOs, NASA commissioned a study of the best methods for seeking out alien life. The resulting report argued for using radio telescopes to listen for the kinds of electromagnetic signals that would emanate from an advanced civilization in space. If we still haven’t seen aliens in person, the thinking went, perhaps we might be able to hear them.

That report landed in the lap of a young astronomer named Jill Tarter, who, like Hynek, had started her career observing distant stars.

In “Making Contact: Jill Tarter and the Search for Extraterrestrial Intelligence,” science journalist Sarah Scoles writes that the astronomer was instantly “converted.” As Tarter told Scoles, “I just knew I’d found the right place, never having thought about it before.” Whereas her work on stars had felt distant and abstruse, SETI gave Tarter a sense of purpose. She went on to direct the first targeted effort to detect extraterrestrial signals and helped found the SETI Institute — now an authority on the search for alien life.

“There was a feeling of connectedness,” Tarter said of this research. “I was doing something that could impact people’s lives profoundly in a short time.”

It’s a noble motivation, and Scoles — who narrates her story in a warm, chatty tone — clearly thinks Tarter is a hero. But the SETI pioneer’s biggest enemies are decidedly prosaic: narrow-minded, sexist male colleagues who try to tell Tarter she doesn’t belong in science; sneering politicians who deny SETI funding to make a political point; seemingly exotic radio signals that turn out to come from ordinary satellites.

Tarter is now celebrated as a pioneer and a feminist icon; she was the inspiration for Jodie Foster’s character in the movie “Contact.” But her story lacks a triumphant ending. She retired in 2012, never having heard the signal she spent her life listening for.

SETI research is a far cry from UFOlogy. But it’s impossible to ignore the similarities between Tarter and Hynek. Both were ordinary astronomers who happened upon the alien question and never let go, regardless of the indifference, derision and outright hostility they encountered. Both devoted their lives to the idea that, as the saying goes, absence of evidence isn’t evidence of absence. Even though absence is all either ever found.

Which brings us back to Fermi’s paradox. More than a half century of sustained scientific research has uncovered neither hide nor hair — or whatever — of extraterrestrial life. Does that mean there’s nothing to be found?

“Aliens: The World’s Leading Scientists on the Search for Extraterrestrial Life” lays out the case for optimism in a collection of essays. The world in which this book was published is one that Hynek and Tarter helped make. Chris French, the head of anomalistic psychology research at Goldsmiths, University of London, uses Hynek’s “close encounters” scale to discuss psychological phenomena that can explain such experiences. Two of the essays were written by scientists at Tarter’s SETI Institute.

The other contributors include experts from astronomy, cosmology, planetary science and genetics, as well as fields that didn’t even exist when Hynek and Tarter began their work — astrobiology and exoplanet research. Together, they provide an overview of where the search for alien life now stands.

Advances in biology on Earth have expanded our notion of where and how life can thrive. Meanwhile, exploration of space has identified places in our solar system and beyond that could be (or once were) hospitable to alien organisms. Mars used to boast an atmosphere and flowing water; the moons of Jupiter and Saturn harbor hidden subsurface oceans and liquid methane lakes. Our growing catalogue of exoplanets suggests that most stars in the galaxy host planets on which life could conceivably form. When the James Webb Space Telescope launches in 2018, scientists will be able to probe the atmospheres of those planets in pursuit of “biosignatures” — molecules that are thought to signal the presence of life.

No one has an answer to the question: “Where is everybody?” But scientists do have plenty of places to look. Perhaps, someday in the not-too-distant future, they’ll receive that long-awaited radio beacon from a distant galaxy. Or look through a microscope at a water sample from an ocean moon and find microbes swimming around. Or detect a haze of “biosignatures” in the atmosphere of an alien world.

Or, hey, maybe an unidentified flying object will appear suddenly in the sky one day when we least expect it. A crowd will gather, a hatch will open and, finally, a little green man will step out to reassure us we’re not alone.

The Close Encounters Man

How One Man Made the World Believe in UFOs

By Mark O’Connell

Dey Street.

403 pp. $17.99 paperback

Making Contact

Jill Tarter and the Search for Extraterrestrial Intelligence

By Sarah Scoles

Pegasus. 288 pp. $27.95

Aliens

The World’s Leading Scientists on the Search for Extraterrestrial Life